A composite right/left-handed transmission line (hereinafter, referred to as a CRLH transmission line) is known as one of metamaterials. The CRLH transmission line is configured by substantially periodically inserting capacitive elements in a series branch of the line and substantially periodically inserting inductive elements in shunt branches of the line at intervals sufficiently smaller than a wavelength so as to have negative effective permeability and a negative effective dielectric constant in a predetermined frequency band. Recently, a non-reciprocal phase-shift CRLH transmission line obtained by adding a non-reciprocal transmission function to the CRLH transmission line has been proposed (For example, see Patent Documents 1 to 3). The non-reciprocal phase-shift CRLH transmission line can show a positive refractive index when electromagnetic waves having an identical frequency propagate in the forward direction and can show a negative refractive index when the electromagnetic waves propagate in the backward direction.
The size of a transmission line resonator can be freely changed without changing the resonance frequency by configuring the resonator using the non-reciprocal phase-shift CRLH transmission line. Further, the electromagnetic field distribution on the resonator is similar to the electromagnetic field distribution of a travelling wave resonator. Therefore, it is possible to configure a pseudo-travelling wave resonator in which the amplitude of the electromagnetic field is uniform and the phase of the electromagnetic field linearly changes at a constant gradient along the line by using the transmission line resonator using the non-reciprocal phase-shift CRLH transmission line. At that time, the phase gradient of the electromagnetic field distribution on the resonator is determined depending on non-reciprocal phase-shift characteristic of the transmission line configuring the resonator. Hereinafter, a transmission line apparatus using the non-reciprocal phase-shift CRLH transmission line is referred to as anon-reciprocal transmission line apparatus.
For the last dozen years, metamaterials have been a very interesting and important theme in the field of application to an antenna. So far, a non-reciprocal CRLH metamaterial has been proposed for the purpose of application to a directional leaky wave antenna using the CRLH transmission line. In addition, recently, an antenna based on a pseudo-travelling wave resonator greatly advanced from a zeroth-order resonator (for example, see Patent Document 1) has been proposed, and the gain and directional pattern of the antenna based on the pseudo-travelling wave resonator have increased compared to those of a conventional leaky wave antenna although the size of the antenna based on the pseudo-travelling wave resonator is more compact.
Many of the non-reciprocal transmission line apparatuses having been proposed so far adopt a structure where a vertically magnetized ferrite rod is embedded under a strip line at the center of a composite right/left-handed transmission line apparatus constituted of a conventional microstrip line. At that time, the direction of a radiation beam from an antenna apparatus provided with a pseudo-travelling wave resonator constituted of a non-reciprocal transmission line apparatus is determined depending on the phase gradient of the electromagnetic field distribution on the resonator. In addition, in a case where ferrite is soft magnetic material, the non-reciprocal phase-shift characteristic of the line changes by changing the magnitude or the direction of the externally applied magnetic field, and as a result, beam scanning can be performed.